Image processing apparatus, image processing method, and program

ABSTRACT

An apparatus includes an image-forming unit configured to form an image, a measuring unit configured to measure the image, a control unit configured to control execution of single-color calibration to correct reproduction characteristics of a single-color formed by the image-forming unit based on a measuring result of a single-color image formed with a single-color recording agent, and execution of multi-color calibration to correct reproduction characteristics of a multi-color formed by the image-forming unit based on a measuring result of a multi-color image formed with a plurality of color recording agents, and an evaluation unit configured to evaluate single-color reproduction characteristics with reference to a target value usable to evaluate the single-color reproduction characteristics by measuring the single-color image after execution of the single-color calibration. The control unit is configured to correct reproduction characteristics of a multi-color by performing the multi-color calibration after the evaluation unit has completed the evaluation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus and animage processing method that can correct a color of an image to beoutput from a printer, and a program that can generate image processingparameters.

2. Description of the Related Art

The recent improvement in performance of electrophotographic apparatusescan realize high image quality comparable to that of a printing machine.However, the instability of each electrophotographic apparatus tends tocause a color variation that is larger than that of a printing machine.

In general, a “single-color” calibration technique is conventionallyavailable for an electrophotographic apparatus. The “single-color”calibration technique includes generating a look-up table (LUT) usableto correct one-dimensional gradation characteristics corresponding toeach of cyan, magenta, yellow, and black (hereinafter, simply referredto as C, M, Y, and K) toners. The LUT is a table that indicates outputdata corresponding to respective input data segmented at specificintervals. Using the LUT is useful in expressing nonlinearcharacteristics to which no calculation formula is available. Further,the “single-color” is a color that is producible using a single toner ofC, M, Y, or K. Performing the single-color calibration is useful tocorrect single-color reproduction characteristics (e.g., maximum densityand gradation).

Further, as discussed in Japanese Patent Application Laid-Open No.2011-254350, a “multi-color” calibration technique using afour-dimensional LUT is conventionally proposed. The “multi-color” is acomposite color that is reproducible using a plurality of toners of red,green, and blue or gray (based on CMY). Especially, according toelectrophotography, even when a one-dimensional LUT is used to correctsingle-color gradation characteristics, a nonlinear difference tends tooccur if a plurality of toners is used to express a “multi-color.”Performing the multi-color calibration is useful to correct multi-colorreproduction characteristics, which can be expressed by a combination(e.g., a superposition) of a plurality of color toners.

A processing procedure including a “multi-color” calibration isdescribed below. The processing includes printing patches on a recordingmedium (e.g., a paper) based on single-color chart data that is usableto perform the “single-color” calibration and reading the printedpatches with a scanner or a sensor. The processing further includescomparing read patch data with target values having been set beforehandand generating a one-dimensional LUT usable to correct differencesbetween read patch data and the target values. The processing furtherincludes printing patches on a recording medium based on multi-colorchart data that reflects the obtained one-dimensional LUT to perform the“multi-color” calibration and reading the printed patches with thescanner or the sensor. The processing includes comparing the read patchdata with target values having been set beforehand and generating afour-dimensional LUT usable to correct differences between read patchdata and the target values.

As mentioned above, it is conventionally feasible to realize highlyaccurate correction by performing the “multi-color” calibration in sucha way as to correct multi-color characteristics that cannot be correctedby the “single-color” calibration.

However, according to the above-mentioned technique, the multi-colorcalibration can be started on condition that gradation characteristicshave been already corrected in the single-color calibration. In otherwords, it is required to complete the single-color calibration beforestarting the multi-color calibration. Therefore, a long processing timeis required to accomplish the multi-color calibration.

For example, if it is determined that an image obtained after themulti-color calibration is insufficient in image quality, it isdifficult to identify a failure having occurred in the single-colorcalibration or the multi-color calibration. Accordingly, it is necessaryto re-execute the single-color calibration and the multi-colorcalibration in this order. The working time for the entire calibrationprocessing greatly increases.

On the other hand, constantly restarting the multi-color calibrationwhile skipping the single-color calibration may be useful to reduce theprocessing time. However, in a case where the single-color calibrationhas not been successfully completed, the correction accuracy willdeteriorate significantly in the multi-color calibration to be performedsubsequently.

From the reason described above, the multi-color calibration may not beeasy to use for a user in a specific situation.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, an image processingapparatus includes an image forming unit configured to form an image; ameasuring unit configured to measure the image formed by the imageforming unit; a control unit configured to control execution of asingle-color calibration to be performed to correct reproductioncharacteristics of a single-color formed by the image forming unit basedon a measuring result obtained when the measuring unit measures asingle-color image formed by the image forming unit with a single-colorrecording agent, and execution of a multi-color calibration to beperformed to correct reproduction characteristics of a multi-colorformed by the image forming unit based on a measuring result obtainedwhen the measuring unit measures a multi-color image formed by the imageforming unit with a plurality of color recording agents; and anevaluation unit configured to evaluate the single-color reproductioncharacteristics with reference to a target value usable to evaluate thesingle-color reproduction characteristics by causing the measuring unitto measure the single-color image formed by the image forming unit afterthe single-color calibration has been executed by the control unit,wherein the control unit is configured to correct reproductioncharacteristics of a multi-color by performing the multi-colorcalibration after the evaluation unit has completed the evaluation.

The present invention is applicable to an image processing apparatusthat can perform both single-color calibration processing andmulti-color calibration processing. The image processing apparatusaccording to the present invention evaluates characteristics correctedin the single-color calibration at the time when the single-colorcalibration has completed. The image processing apparatus according tothe present invention determines whether to perform the multi-colorcalibration according to an evaluation result.

Thus, the image processing apparatus according to the present inventioncan prevent the working time from increasing when it is necessary tore-execute the calibration processing because of inappropriateness inthe quality of an image printed after completing the multi-colorcalibration.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 illustrates a configuration of an image processing system.

FIG. 2 is a flowchart illustrating an example procedure of imageprocessing.

FIG. 3 is a flowchart illustrating an example procedure of single-colorcalibration processing.

FIG. 4 is a flowchart illustrating an example procedure of multi-colorcalibration processing.

FIGS. 5A to 5C illustrate a plurality of charts that can be used in thesingle-color calibration and the multi-color calibration.

FIG. 6 is a flowchart illustrating an example procedure of calibrationprocessing according to a first exemplary embodiment.

FIG. 7 illustrates a plurality of charts that can be used in themulti-color calibration according to the first exemplary embodiment.

FIG. 8 illustrates an example of coefficients usable to evaluategradation characteristics according to the first exemplary embodiment.

FIG. 9 illustrates an example of a user interface (UI) screen thatincludes an error message to be displayed based on a gradationcharacteristics evaluation result according to the first exemplaryembodiment.

FIG. 10 is a flowchart illustrating an example procedure of calibrationprocessing according to a second exemplary embodiment.

FIG. 11 is a flowchart illustrating an example procedure of calibrationprocessing according to a third exemplary embodiment.

FIG. 12 illustrates a menu screen that enables a user to select thesingle-color calibration and/or the multi-color calibration.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

An image processing system according to a first exemplary embodiment ofthe present invention is described below. In the present exemplaryembodiment, the system evaluates single-color characteristics to becorrected in the single-color calibration when the system reads a chartdedicated to the multi-color calibration.

FIG. 1 illustrates a configuration of the image processing systemaccording to the present exemplary embodiment. A multi function printer(MFP) 101 is an image processing apparatus that can form images usingcyan, magenta, yellow, and black (hereinafter, referred to C, M, Y, andK) toners. The MFP 101 is connected to other network devices via anetwork 123. Further, a personal computer (PC) 124 is connected to theMFP 101 via the network 123. The PC 124 includes a printer driver 125that can transmit print data to the MFP 101.

The MFP 101 is described in detail below. A network interface (I/F) 122can receive print data. A controller 102 includes a central processingunit (CPU) 103, a renderer 112, and an image processing unit 114. TheCPU 103 includes an interpreter 104 that can interpret a pagedescription language (PDL) portion included in the received print dataand generate intermediate language data 105.

A color management system (CMS) 106 can perform color conversion using asource profile 107 and a destination profile 108, and can generateintermediate language data (post CMS) 111. Profile information usable inthe color conversion to be performed by the CMS 106 is described below.The source profile 107 can convert a device-dependent color space (e.g.,RGB and CMYK) into a device-independent color space (e.g., L*a*b*(hereinafter, referred to as “Lab”) and XYZ). Lab is the color spacespecified by the CIE (Commission Internationale del'Eclairage=International Commission on Illumination). XYZ is adevice-independent color space that is similar to Lab, which can expressa color with three types of stimulus values. Further, the destinationprofile 108 is a profile that can convert a device-independent colorspace into a device (e.g., printer 115)-dependent CMYK color space.

On the other hand, another color management system (CMS) 109 can performcolor conversion using a device link profile 110 and can generateintermediate language data (post CMS) 111. The device link profile 110is a profile that can directly convert a device-dependent color space(e.g., RGB or CMYK) into the device (e.g., printer 115)-dependent CMYKcolor space. Selection of the CMS 106 or the CMS 109 is determinedaccording to a setting by the printer driver 125.

In the present exemplary embodiment, either of color management systems(106 and 109) is provided according to the type of each profile (107,108, or 110). However, it is useful that a single CMS is configured toprocess a plurality of types of profiles. Further, the type of eachprofile is not limited to the example described in the present exemplaryembodiment. Any type of profile can be used if it can use thedevice-dependent CMYK color space of the printer 115.

The renderer 112 can generate raster image 113 based on the generatedintermediate language data (post CMS) 111. The image processing unit 114can perform image processing on the raster image 113 or an image read bya scanner 119. The image processing unit 114 is described in detailbelow.

The printer 115, which is connected to the controller 102, is a printercapable of forming an image on a paper using C, M, Y, and K color tonersbased on output data. The printer 115 includes a paper feeding unit 116that can feed a paper as a recording material, a paper discharge unit117 that can discharge a paper on which an image is formed, and ameasuring unit 126.

The measuring unit 126 includes a sensor 127 that can acquire a spectralreflectance value and a device-independent color space (e.g., Lab orXYZ) value. The printer 115 includes a CPU 129 that can control variousoperations to be performed by the printer 115. The CPU 129 can controlthe measuring unit 126. The measuring unit 126 reads a patch image froma recording medium (e.g., a paper) printed by the printer 115 with thesensor 127. The measuring unit 126 transmits numerical informationacquired from the patch image to the controller 102. The controller 102performs calculations using the numerical information received from themeasuring unit 126. The controller 102 performs the single-colorcalibration or the multi-color calibration based on a calculationresult.

The MFP 101 includes a display device 118, which is operable as a userinterface (UI) having the capability of displaying an instructionmessage directed to a user or an operational state of the MFP 101. Thedisplay device 118 can be used in the single-color calibration or themulti-color calibration.

The scanner 119 includes an auto document feeder. The scanner 119 isconfigured to irradiate a bundle of paper documents or a piece of paperdocument with light emitted from a light source (not illustrated) andcause a lens to form a reflected document image on a solid-state imagesensor, such as a charge coupled device (CCD) sensor. Then, the scanner119 obtains a raster image reading signal, as image data, from thesolid-state image sensor.

The MFP 101 includes an input device 120 that is operable as aninterface that can receive instructions input by a user. The inputdevice can be partly configured as a touch panel that is integrated withthe display device 118.

The MFP 101 includes a storage device 121 that stores data processed bythe controller 102 and data received from the controller 102.

A measuring device 128 is an external measuring device that is connectedto a network or to the PC 124. Similar to the measuring unit 126, themeasuring device 128 can acquire a spectral reflectance value and adevice-independent color space (e.g., Lab or XYZ) value.

Next, an example of processing that can be performed by the imageprocessing unit 114 is described with reference to FIG. 2. FIG. 2 is aflowchart illustrating an example of image processing applied to theraster image 113 or an image read by the scanner 119. The imageprocessing unit 114 includes an Application Specific Integrated Circuit(ASIC) (not illustrated) that can execute the processing illustrated inFIG. 2.

In step S201, the image processing unit 114 receives image data. Then,in step S202, the image processing unit 114 determines whether thereceived data is scanning data received by the scanner 119 or the rasterimage 113 received from the printer driver 125.

If the received data is not the scanning data (NO in step S202), thereceived data is the raster image 113 having been bitmap rasterized bythe renderer 112. The raster image 113 becomes a CMYK image 211 (whichhas been converted into printer device-dependent CMYK by the CMS).

If the received data is the scanning data (YES in step S202), thereceived data is a RGB image 203. Therefore, in step S204, the imageprocessing unit 114 performs color conversion processing to generate acommon RGB image 205. The common RGB image 205 is an image defined in adevice-independent RGB color space and can be converted into adevice-independent color space (e.g., Lab) through calculations.

On the other hand, in step S206, the image processing unit 114 performscharacter determination processing to generate character determinationdata 207. In the present exemplary embodiment, the image processing unit114 detects an edge of the image to generate the character determinationdata 207.

Next, in step S208, the image processing unit 114 performs filterprocessing on the common RGB image 205 using the character determinationdata 207. In the present exemplary embodiment, the image processing unit114 differentiates the filter processing applied to a character portionand the filter processing applied to the remaining portion.

Next, in step S209, the image processing unit 114 performs backgroundcolor removal processing. In step S210, the image processing unit 114performs color conversion processing to generate the CMYK image 211 fromwhich the background has been removed.

Next, in step S212, the image processing unit 114 performs multi-colorcorrection processing using a 4D-LUT 217. The 4D-LUT 217 is afour-dimensional look up table (LUT) that is usable to convert acombination of C, M, Y, and K signal values into a combination ofdifferent C, M, Y, and K signal values in outputting respective toners.The 4D-LUT 217 can be generated by “the multi-color calibration”described below. Thus, it becomes feasible to correct a “multi-color”,i.e., a composite color obtainable using a plurality of toners, withreference to the 4D-LUT.

If the multi-color correction processing in step S212 is completed, thenin step S213, the image processing unit 114 corrects single-colorgradation characteristics of respective C, M, Y, and K colors, using a1D-LUT 218. The 1D-LUT 218 is a one-dimensional lookup table (LUT) thatis usable to correct each of the C, M, Y, and K colors (i.e.,single-colors). The 1D-LUT 218 can be generated by “the single-colorcalibration” described below.

Finally, in step S214, the image processing unit 114 performs halftoneprocessing (e.g., screen processing and/or error diffusion processing)to generate a CMYK image (binary value) 215. Then, in step S216, theimage processing unit 114 transmits the processed image data to theprinter 115.

An example of the “single-color calibration” for correcting single-colorgradation characteristics to be output from the printer 115 is describedwith reference to FIG. 3. Performing the single-color calibration isuseful to correct single-color reproduction characteristics (e.g.,maximum density characteristics and gradation characteristics). Thecolor reproduction characteristics corresponding to respective C, M, Y,and K toners used by the printer 115 can be corrected together when thecalibration is performed. More specifically, the processing of theflowchart illustrated in FIG. 3 can be performed simultaneously forrespective C, M, Y, and K colors.

FIG. 3 is a flowchart illustrating a processing procedure for generatingthe 1D-LUT 218 to be used to correct the single-color gradationcharacteristics. The CPU 103 performs the processing of the flowchartillustrated in FIG. 3. The storage device 121 stores the generated1D-LUT 218. The display device 118 displays a UI screen that includes aninstruction message directed to a user. The input device 120 receives aninstruction from the user.

In step S301, the CPU 103 acquires chart data “A” 302 from the storagedevice 121. The chart data “A” 302 is usable to correct the maximumdensity of each single color. The chart data “A” 302 includes signalvalues (e.g., 255) based on which maximum density data of respective C,M, Y, and K “single-colors” can be obtained.

Next, in step S303, the CPU 103 causes the image processing unit 114 toperform image processing on the chart data “A” 302. The CPU 103 causesthe printer 115 to print a chart “A” 304. FIG. 5A illustrates a chartexample 501 printed based on the chart data “A” 302. The chart example501 includes four patches 502, 503, 504, and 505 of C, M, Y, and Kcolors, respectively, which have been printed at their maximumdensities. In this case, the image processing unit 114 performs only thehalftone processing in step S214. The image processing unit 114 does notperform the 1D-LUT correction processing in step S213 and does notperform the 4D-LUT correction processing in step S212.

Next, in step S305, the CPU 103 measures the density of the printedproduct of the chart “A” 304 with the scanner 119 or the sensor 127provided in the measuring unit 126, and obtains a measurement value “A”306. The measurement value “A” 306 indicates a density value of each ofthe C, M, Y, and K colors. Next, in step S307, the CPU 103 corrects themaximum density of the measurement value “A” 306 of each color withreference to the measurement value “A” 306 and a target value “A” 308 ofthe maximum density value having been set beforehand. In the presentexemplary embodiment, the CPU 103 adjusts a device setting value (e.g.,laser output or development bias) of the printer 115 in such a way as toequalize the maximum density with the target value “A” 308.

Next, in step S309, the CPU 103 acquires chart data “B” 310 from thestorage device 121. The chart data “B” 310 includes signal values thatrepresent “single-color” gradation data of C, M, Y, and K. A chart “B”312 including patches printed on a recording medium based on the chartdata “B” 310 is described below with reference to FIG. 5B. A chartexample 506 illustrated in FIG. 5B is a printed product of the chart “B”312 including a plurality of patches printed on a recording medium basedon the chart data “B” 310. The chart example 506 illustrated in FIG. 5Bincludes four patch groups 507, 508, 509, and 510 each including aplurality of gradation data of C, M, Y, and K colors, respectively.

Next, in step S311, the CPU 103 causes the image processing unit 114 toperform image processing on the chart data “B” 310. The CPU 103 causesthe printer 115 to print the chart “B” 312. In this case, the imageprocessing unit 114 performs only the halftone processing in step S214.The image processing unit 114 does not perform the 1D-LUT correctionprocessing in step S213 and does not perform the 4D-LUT correctionprocessing in step S212. The printer 115 is already subjected to themaximum density correction in step S307. Therefore, in this state, themaximum density is substantially equal to the target value “A” 308.

Next, in step S313, the CPU 103 performs measurement using the scanner119 or the sensor 127, and obtains a measurement value “B” 314. Themeasurement value “B” 314 indicates a density value that is obtainablefrom the gradation of each of C, M, Y, and K colors. Next, in step S315,the CPU 103 generates the 1D-LUT 218 to be used to correct thesingle-color gradation characteristics based on the measurement value“B” 314 and a target value “B” 316 having been set beforehand.

Next, an example of the “multi-color calibration” for correctingmulti-color characteristics to be output from the printer 115 isdescribed with reference to FIG. 4. Performing the multi-colorcalibration is useful to correct multi-color reproductioncharacteristics (which can be expressed using a combination (orsuperposition) of a plurality of color toners). The CPU 103 provided inthe controller 102 can perform the following processing. The storagedevice 121 stores the acquired 4D-LUT 217. Further, the display device118 displays a UI screen that includes an instruction message directedto a user, and the input device 120 receives an instruction from theuser.

The multi-color calibration follows the single-color calibration, aspost-processing for correcting a multi-color to be output from theprinter 115. Accordingly, it is desired to perform the multi-colorcalibration immediately after completing the single-color calibration.

In step S401, the CPU 103 acquires information about “multi-color” chartdata “C” 402 from the storage device 121. The chart data “C” 402 isusable to correct each multi-color. The chart data “C” 402 includessignal values of a “multi-color” that is a combination of C, M, Y, and Kcolors. A chart “C” 404 including a plurality of patches printed on arecording medium based on the chart data “C” 402 is described below withreference to FIG. 5C. FIG. 5C illustrates a chart example 511 printedbased on the chart data “C” 402. A patch 512 and all patches printed onthe chart example 511 is a multi-color patch configured as a combinationof C, M, Y, and K colors.

Next, in step S403, the CPU 103 causes the image processing unit 114 toperform image processing on the chart data “C” 402 and causes theprinter 115 to print the chart “C” 404. In the multi-color calibration,to correct device multi-color characteristics after completing thesingle-color calibration, the image processing unit 114 performs imageprocessing using the 1D-LUT 218 generated in the single-colorcalibration.

Next, in step S405, the CPU 103 measures a multi-color of the printedproduct of the chart “C” 404 with the scanner 119 or the sensor 127provided in the measuring unit 126, and acquires a measurement value “C”406. The measurement value “C” 406 indicates multi-color characteristicsof the printer 115 at time when the single-color calibration has beencompleted. Further, the measurement value “C” 406 is defined in adevice-independent color space. In the present exemplary embodiment, themeasurement value “C” 406 is a Lab value. If the scanner 119 is used inthe measurement, the CPU 103 converts an obtained RGB value into a Labvalue using a 3D-LUT (not illustrated).

Next, in step S407, the CPU 103 acquires a Lab→CMY 3D-LUT 409 from thestorage device 121 and generates a Lab→CMY 3D-LUT (corrected) 410 insuch a way as to reflect a difference between the measurement value “C”406 and a target value “C” 408 having been set beforehand. The Lab→CMY3D-LUT is a three-dimensional LUT usable to output a CMY value thatcorresponds to an input Lab value.

As one of generation methods, the CPU 103 can add a difference betweenthe measurement value “C” 406 and the target value “C” 408 to aninput-side Lab value of the Lab→CMY 3D-LUT 409 and can performinterpolation calculation on the difference reflecting Lab value usingthe Lab→CMY 3D-LUT 409. Then, as a result of the interpolationcalculation, the CPU 103 can generate the Lab→CMY 3D-LUT (corrected)410.

Next, in step S411, the CPU 103 acquires a CMY→Lab 3D-LUT 412 from thestorage device 121 and performs calculations using the Lab→CMY 3D-LUT(corrected) 410. Then, as a calculation result, the CPU 103 generates aCMYK→CMYK 4D-LUT 217. The CMY→Lab 3D-LUT is a three-dimensional LUTusable to output a Lab value that corresponds to an input CMY value.

A method for generating the CMYK→CMYK 4D-LUT 217 is described below. TheCPU 103 generates a CMY→CMY 3D-LUT based on the CMY→Lab 3D-LUT 412 andthe Lab→CMY 3D-LUT (corrected) 410. Next, the CPU 103 generates theCMYK→CMYK 4D-LUT 217 in such away as to equalize an input value of Kwith an output value of K. The CMY→CMY 3D-LUT is a three-dimensional LUTusable to output a corrected CMY value that corresponds to an input CMYvalue.

FIG. 6 is a flowchart illustrating an example procedure of calibrationprocessing according to the present exemplary embodiment. The CPU 103provided in the controller 102 performs the following processing. Thestorage device 121 stores the acquired data. Further, the display device118 displays a UI screen that includes an instruction message directedto a user. The input device 120 receives an instruction from the user.

First, in step S601, the CPU 103 performs single-color calibrationprocessing to correct the maximum density. FIG. 12 illustrates a UIscreen 1201 that enables a user to select the single-color calibrationand/or the multi-color calibration. The display device 118 displays theUI screen 1201 illustrated in FIG. 12. A button 1202 is operable toinput an instruction of starting the single-color calibration. A button1203 is operable to input an instruction of starting the multi-colorcalibration. Further, a button 1204 is operable to input an instructionof performing the multi-color calibration after completing thesingle-color calibration.

In step S601, a user presses the button 1204 of the color correctionmenu illustrated in FIG. 12 to perform the single-color calibration andthe multi-color calibration successively. Alternatively, the CPU 103automatically performs the single-color calibration and the multi-colorcalibration successively at a predetermined timing. For example, the CPU103 automatically starts the sequential calibration processing when apredetermined time has elapsed or a predetermined number of papers havebeen used in the printing, or when a power source is activated.

First, the CPU 103 starts the single-color calibration to correct themaximum density of an image formed with a single-color toner. Theprocessing to be performed in step S601 is similar to the processingperformed in steps S301 to S307 illustrated in FIG. 3 and thereforeredundant description thereof will be avoided.

Next, in step S602, the CPU 103 performs single-color calibrationprocessing to correct the gradation. More specifically, the CPU 103generates the 1D-LUT 218 that can be used to correct the gradation ofthe image formed with the single-color toner. The processing to beperformed in step S602 is similar to the processing performed in stepsS309 to S315 illustrated in FIG. 3 and therefore redundant descriptionthereof will be avoided.

Next, in step S603, the CPU 103 acquires information about the chartdata “D” 604 relating to “multi-color” and “gradation characteristicsevaluation” data from the storage device 121.

Next, in step S605, the CPU 103 causes the image processing unit 114 toperform image processing on the chart data “D” 604 and causes theprinter 115 to output a chart “D” 606. As mentioned above, the CPU 103starts the multi-color calibration to correct a multi-color to be outputfrom the printer 115 after completing the single-color calibration.Accordingly, the image processing unit 114 performs the image processingusing the 1D-LUT 218 generated in the single-color calibration.

FIG. 7 illustrates an example 701 of the chart “D” 606 that includes aplurality of patches printed on a recording medium based on the chartdata “D” 604. The chart 701 includes a group of patches that can be usedin multi-color correction (see a portion 702 surrounded with a dottedline), which are data constituted by “multi-color” signal values (i.e.,a combination of C, M, Y, and K colors), similar to the chart data “C”402. The chart 701 further includes a group of patches usable toevaluate single-color gradation characteristics of the printer 115 (seea portion 703 surrounded with a dotted line), which can be printed usingsingle-color (C, M, Y, or K) data. The number of patches in this casemay be smaller than that of the chart data “B” 310 because it is notintended to correct the gradation characteristics.

Further, from the reason described below, it is useful that the chart701 includes additional data indicating signal values representingmaximum densities of C, M, Y, and K colors. In the present exemplaryembodiment, the CPU 103 performs multi-color correction processing andevaluates gradation characteristics using patches printed on a piece ofpaper. Therefore, a smaller number of patches are used to evaluategradation characteristics, as described below. However, it is useful toprint patches to be used in the multi-color correction on a chart sheetand print patches to be used in evaluating gradation characteristics onanother chart sheet.

Next, in step S607, the CPU 103 measures the chart “D” 606 with thescanner 119 or the sensor 127 provided in the measuring unit 126, andacquires a the measurement value “D” 608. The measurement value “D” 608indicates multi-color characteristics and single-color gradationcharacteristics of the printer 115 at the time when the single-colorcalibration has been completed. Further, multi-color characteristics ofthe measurement value “D” 608 can be expressed in a device-independentcolor space. In the present exemplary embodiment, the measurement value“D” 608 is a Lab value. Further, the density represents the gradationcharacteristics of the measurement value “D” 608. If the scanner 119 isused in the measurement, the CPU converts an obtained RGB value into aLab value or a density value using a 3D-LUT (not illustrated).

Next, in step S609, the CPU 103 extracts single-color density data to beused in the gradation characteristics evaluation from the measurementvalue “D” 608. Then, in step S610, the CPU 103 evaluates single-colorreproduction characteristics based on the extracted single-color densitydata, with reference to a predetermined target value “D” 611, anevaluation coefficient 612, and an evaluation threshold value 613.

First, a target to be evaluated in the present exemplary embodiment, asthe single-color reproduction characteristics, is gradationcharacteristics of each single-color to be output from the printer 115.The CPU 103 determines whether the gradation characteristics have beenappropriately corrected in the previously executed single-colorcalibration.

In the present exemplary embodiment, the target value “D” 611 is similarto the target value “B” 316 used in generating the 1D-LUT 218 for thesingle-color gradation correction in step S315 of the flowchart (i.e.,the single-color calibration execution flow) illustrated in FIG. 3.Alternatively, the target value “D” 611 can be another value that isdifferent from the target value “B” 316, because the chart to be used inthe single-color calibration processing may be different from the datato be used in evaluating the single-color gradation characteristics. Thetarget value used in the above-mentioned evaluation is referred to as a“target value usable to evaluate the single-color reproductioncharacteristics.”

Further, for example, the evaluation includes measuring eachsingle-color image output from the printer 115 after the single-colorcalibration has been completed, obtaining a difference value between themeasurement value “D” 608 and its target value “D” 611, and determiningwhether the obtained difference value is greater than a threshold value.

As another example, it is useful to obtain a ratio of the measurementvalue “D” 608, obtainable when measuring each single-color image outputfrom the printer 115 after the single-color calibration has beencompleted, to its target value “D” 611, and use the obtained ratio inthe evaluation. In this case, the obtained ratio can be referred to indetermining whether the measurement value “D” 608 is adjacent to thetarget value. For example, an evaluation can be determined by checkingwhether the ratio is greater than a threshold value.

As another example, it is useful to perform an evaluation using a valuethat can be acquired based on the comparison between the measurementvalue “D” 608 and its target value “D” 611.

Hereinafter, example evaluation processing including obtaining adifference value between the measurement value “D” 608 and its targetvalue “D” 611 and determining whether the obtained difference value isgreater than a threshold value is described below.

The target value “D” 611 is compatible with the characteristicsevaluation data of the chart data “D” 604. In general, if an obtainedmeasurement value “D” 608 is adjacent to its target value “D” 611, thegradation characteristics can be evaluated as good. More specifically,it means that the gradation characteristics have been appropriatelycorrected in the previously executed single-color calibration.

On the other hand, if an obtained measurement value “D” 608 greatlydeviates from its target value “D” 611, it means that the gradationcharacteristics have not been appropriately corrected in the previouslyexecuted single-color calibration. The above-mentioned evaluation resultis usable in determining whether performing the single-color calibrationagain is necessary to correct the gradation characteristics.

FIG. 8 is a table 801 including a plurality of sets of evaluationcoefficients, which are applicable to four (i.e., C, M, Y, and K) typesof colors. The evaluation coefficients are classified beforehandconsidering the color and the density. If a numerical value of theevaluation coefficient is high, it means that the corresponding color ordensity has a great influence on a characteristics evaluation result. Inthe table illustrated in FIG. 8, the density is classified into any oneof three classes (i.e., low density, middle density, and high density)because the “gradation characteristics evaluation” data of the chartdata “D” 604 is classified into any one of three levels.

According to the table 801, the highest evaluation coefficient is setfor the high-density K color. More specifically, if the high-density Kcolor deviates from the target value, an evaluation result of the“gradation characteristics evaluation” tends to become NG. Accordingly,if the high-density K color deviates from the target value, it will behighly necessary to perform the single-color calibration before startingthe multi-color calibration.

A method for determining evaluation coefficients is described below.When the evaluation target is the “maximum density”, it is useful toreduce the signal value of the CMYK image 211 if the measured patchdensity is excessively high. Accordingly, the measured patch density canbe corrected in the 4D-LUT correction processing to be performed in themulti-color calibration processing (see step S212).

On the other hand, in a case where the measured patch density isexcessively low, the signal value of the CMYK image 211 is alreadymaximized. Accordingly, increasing the signal value is difficult. Inother words, the correction cannot be performed in the 4D-LUT correctionprocessing (see step S212). In this case, the correction requiresperforming the maximum density correction processing in the single-colorcalibration (see step S601). Accordingly, if the maximum densitycorrection result is inappropriate, it is necessary to re-execute thesingle-color calibration. From the reason described above, theevaluation of the maximum density is prioritized. The maximum densitygives a greatest influence on the evaluation result.

From the reason described above, it is desired that maximum density datais included in the data 703 to be used in evaluating the single-colorgradation characteristics. Further, in general, a color printer isusable for monochrome printing. Therefore, the K color to be used inboth color printing and monochrome printing has a higher evaluationcoefficient. It is useful to change C, M, Y, and K evaluationcoefficients according to the printer usage status that is variabledepending on each user.

For example, if a user who frequently uses the printer in a blackmonochrome print mode instructs the calibration, it is useful to set theK evaluation coefficient to be high. On the other hand, if a user whofrequently uses the printer in a color print mode instructs thecalibration, it is useful to set the C, M, and Y evaluation coefficientsto be high. The evaluation threshold value 613 is a threshold valueusable to evaluate the gradation characteristics. The gradationcharacteristics of a data are evaluated as NG if its value exceeds theevaluation threshold value 613.

As an example method, the following formula (1) is usable to calculate agradation characteristics evaluation value Es.Es=Σ _(i=0) ^(n) C _(i) *|D _(t) −D _(m)|  (1)

n: number of gradation characteristics evaluation data, C_(i):evaluation coefficient, D_(t): target value (density), D_(m):measurement value (density).

The CPU 103 compares the acquired gradation characteristics evaluationvalue Es with the evaluation threshold value 613. If it is determinedthat the gradation characteristics evaluation value Es is equal to orless than the evaluation threshold value 613, the CPU 103 evaluates thegradation characteristics of the printer 115 that has output the chartdata 701 as OK. More specifically, the CPU 103 deems that the gradationcharacteristics have been appropriately corrected in the previouslyexecuted single-color calibration. On the other hand, if the gradationcharacteristics evaluation value Es is greater than the evaluationthreshold value 613, the CPU 103 evaluates the gradation characteristicsas NG. More specifically, the CPU 103 deems that the gradationcharacteristics have not been appropriately corrected in the previouslyexecuted single-color calibration.

If it is determined that the gradation characteristics evaluation resultis NG (yes in step S614), then in step S615, the CPU 103 causes thedisplay device 118 to display a message that recommends a user torestart the single-color calibration. FIG. 9 illustrates a UI screen 901that can be displayed in step S615. The UI screen 901 includes a messageindicating that there is a problem in gradation characteristics (i.e.,the target to be corrected in the single-color calibration).

If the user presses a “Next” button, the CPU 103 causes the displaydevice 118 to display the UI screen 1201 illustrated in FIG. 12 toenable the user to instruct performing the single-color calibrationindependently. Alternatively, the CPU 103 can automatically start thesingle-color calibration even when no instruction is received from theuser.

If it is determined that the gradation characteristics evaluation resultis OK (no in step S614), then in step S616, the CPU 103 performsmulti-color calibration processing. As the button 1204 illustrated inFIG. 12 is already pressed in the beginning of the processing, the CPU103 automatically starts the multi-color calibration processing.Alternatively, it is useful that the CPU 103 waits until the userpresses the button 1203 for confirmation.

The multi-color calibration processing to be performed in step S616 issimilar to the processing performed in steps S407 to S411 illustrated inFIG. 4 and therefore redundant description thereof will be avoided.

Further, if it is determined that the result of the implementedmulti-color calibration is inappropriate, it is useful that the CPU 103exclusively re-executes the multi-color calibration because themeasuring result of the reproduction characteristics (i.e., thegradation characteristics) to be corrected in the single-colorcalibration is already evaluated as being appropriate.

In the present exemplary embodiment, if the gradation characteristicsevaluation result is NG, the CPU 103 forcibly performs the single-colorcalibration processing. However, it is also useful to display a UIscreen that requests a user to determine whether to perform thesingle-color calibration.

Further, the image processing system according to the present exemplaryembodiment evaluates the gradation characteristics for each of the C, M,Y, and K colors. However, it is useful that the image processing systemaccording to the present exemplary embodiment evaluates the gradationcharacteristics of a specific color only. Further, in the presentexemplary embodiment, the number of data to be used in the gradationcharacteristics evaluation is less than the number of data used in thesingle-color calibration. However, the number of data to be used in thegradation characteristics evaluation can be equivalent to or larger thanthe number of data used in the single-color calibration. Further, it isuseful to differentiate the density values to be used in the gradationcharacteristics evaluation for each color.

The image processing system according to the present exemplaryembodiment evaluates gradation characteristics to be corrected in thesingle-color calibration before correcting multi-color reproductioncharacteristics in the multi-color calibration processing. Then, if itis determined that the evaluation result is appropriate, the imageprocessing system according to the present exemplary embodiment performsmulti-color calibration processing. Thus, it becomes feasible to improvethe correction accuracy in the multi-color calibration.

Further, if it is necessary to re-execute the calibration processingbecause of inappropriateness in the quality of an image printed aftercompleting the multi-color calibration, the image processing systemaccording to the present exemplary embodiment can re-execute only themulti-color calibration processing because there is not any problem inthe gradation characteristics. Therefore, it becomes feasible to shortenthe working time in re-executing the calibration processing in a casewhere the correction result was inappropriate in the calibrationincluding at least multi-color calibration.

In the second exemplary embodiment, if it is determined that gradationcharacteristics evaluation performed before starting the multi-colorcalibration processing reveals that the gradation characteristicscorrected in the single-color calibration is inappropriate, the imageprocessing system evaluates the correction result of the maximum densityvalue (i.e., the reproduction characteristics target to be corrected inthe single-color calibration). The image processing system determines anappropriate method according to which the single-color calibration is tobe performed again.

According to the first exemplary embodiment, if the gradationcharacteristics evaluation result is NG at the time when thesingle-color calibration has been completed, the image processing systemperforms the single-color calibration processing again to correct thegradation characteristics.

However, even if the gradation characteristics evaluation result is NG,the correction result of the maximum density (i.e., one of thereproduction characteristics corrected in the previously executedsingle-color calibration) may be appropriate. In this case, the workingefficiency significantly deteriorates if the maximum density correctionis included in the single-color calibration to be performed again.

Accordingly, considering the above-mentioned situation, the imageprocessing system according to the present exemplary embodimentdetermines an appropriate method according to which the single-colorcalibration processing is to be performed with reference to a maximumdensity evaluation result, as described below.

FIG. 10 is a flowchart illustrating an example procedure of theprocessing that can be performed by the image processing systemaccording to the present exemplary embodiment. The CPU 103 provided inthe controller 102 performs the processing of the flowchart illustratedin FIG. 10. The storage device 121 stores the acquired data. Further,the display device 118 displays a UI screen that includes an instructionmessage directed to a user. The input device 120 receives an instructionfrom the user.

Processing to be performed in steps S1001 to S1009 is similar to theprocessing performed in steps S601 to S609 and therefore redundantdescription thereof will be avoided.

In the present exemplary embodiment, the CPU 103 designates gradationcharacteristics and maximum density of each single-color to be outputfrom the printer 115, as target single-color reproductioncharacteristics to be evaluated. Then, the CPU 103 determines whetherthese characteristics have been appropriately corrected in thepreviously executed single-color calibration.

In step S1010, the CPU 103 evaluates the gradation characteristics andthe maximum density based on the extracted single-color density datawith reference to a predetermined target value “D” 1011, an evaluationcoefficient 1012, and an evaluation threshold value 1013. Then, the CPU103 outputs a maximum density evaluation result. The gradationcharacteristics evaluation to be performed by the CPU 103 is similar tothat described in the first exemplary embodiment and therefore redundantdescription thereof will be avoided.

An example of the maximum density evaluation is described below. Maximumdensity evaluation values of respective C, M, Y, and K colors used inthe gradation characteristics evaluation can be used in the maximumdensity evaluation.

In the maximum density evaluation, for example, the CPU 103 uses adifference between a measurement value “D” 1008 and the target value “D”1011. The measurement value “D” 1008 indicates a maximum density valueobtainable when the density of each single-color image output from theprinter 115 is measured after the single-color calibration has beencompleted. Then, the CPU 103 determines whether the obtained differenceis greater than a predetermined threshold value. The target value “D”1011 is similar to the target value “A” 308 having been used to correctthe maximum density in step S307 of the single-color calibrationexecution flow illustrated in FIG. 3.

Further, the evaluation threshold value 1013 is a threshold valuededicated to the maximum density (i.e., a value having been setindependently of the threshold value dedicated to the gradationcharacteristics).

Further, for example, it is useful to use a ratio of the measurementvalue “D” 1008 to the target value “D” 1011 in the maximum densityevaluation. The measurement value “D” 1008 is a value indicating amaximum density value obtainable when the density of each single-colorimage output from the printer 115 is measured after the single-colorcalibration has been completed. The CPU 103 can refer to such a ratio indetermining whether the measurement value “D” 1008 is adjacent to thetarget value “D” 1011. More specifically, in the evaluation, the CPU 103determines whether the ratio of the measurement value “D” 1008 to thetarget value “D” 1011 is greater than a threshold value. Further, anyvalue that is obtainable based on the comparison between the measurementvalue “D” 1008 and the target value “D” 1011 is usable in theevaluation.

In the evaluation described below, the CPU 103 obtains a differencevalue between the measurement value “D” 1008 and the target value “D”1011 and determines whether the obtained difference value is greaterthan a threshold value.

If the measurement value “D” 1008 indicating the obtained maximumdensity is adjacent to the target value “D” 1011, the CPU 103 evaluatesthat the maximum density is appropriate. More specifically, it meansthat the maximum density has been appropriately corrected in thepreviously executed single-color calibration. To the contrary, if themeasurement value “D” 1008 indicating the obtained maximum densitygreatly deviates from the target value “D” 1011, the CPU 103 evaluatesthat the maximum density is inappropriate. More specifically, it meansthat the maximum density has not been appropriately corrected in thepreviously executed single-color calibration. Using the above-mentionedevaluation result, the CPU 103 determines whether performing thesingle-color calibration again is necessary to correct the maximumdensity.

If the maximum density of the density data extracted in step S1009 isequal to or less than the threshold value, a maximum density evaluationresult 1018 becomes OK. The maximum density evaluation result 1018 is anevaluated maximum density that can be output by the printer 115, whichhas printed a chart “D” 1006. More specifically, in this case, the CPU103 determines that the maximum density has been appropriately correctedin the single-color calibration.

On the other hand, if the maximum density of the extracted density datais greater than the threshold value, the maximum density evaluationresult 1018 becomes NG, because the maximum density output from theprinter 115 having printed the chart “D” 1006 greatly deviates from thetarget value. More specifically, it means that the maximum density hasnot been appropriately corrected.

Next, in step S1014, the CPU 103 determines whether the gradationcharacteristics evaluation result of the printer 115 that has printedthe chart “D” 1006 is NG. If it is determined that the gradationcharacteristics evaluation result is OK (no in step S1014), then in stepS1016, the CPU 103 performs multi-color calibration processing.

If it is determined that the gradation characteristics evaluation resultof the printer 115 that has printed the chart “D” 1006 is NG (yes instep S1014), then in step S1015, the CPU 103 causes the display device118 to display a UI screen including an error message. Subsequently, instep S1017, the CPU 103 determines whether the maximum densityevaluation result of the printer 115 that has printed the chart “D” 1006is NG with reference to the maximum density evaluation result 1018. Ifthe maximum density evaluation result is NG (yes in step S1017), namely,if the maximum density correction is insufficient, then in step S1001,the CPU 103 performs the single-color calibration processing again tocorrect the maximum density.

If the maximum density evaluation result is OK (no in step S1017),namely if the maximum density correction has been appropriatelyperformed, then in step S1002, the CPU 103 performs the single-colorcalibration processing again to correct the gradation characteristics.In this case, it is useful that the CPU 103 controls the display device118 to display a UI screen that notifies a user of skipping the maximumdensity correction because the maximum density is currently appropriate.

In this case, to re-execute the single-color calibration, the CPU 103can control the display device 118 to display the UI screen illustratedin FIG. 12 to enable a user to instruct performing the single-colorcalibration again. Alternatively, the CPU 103 can automatically startthe single-color calibration again.

As described above, the image processing system according to the presentexemplary embodiment evaluates the maximum density and the gradationcharacteristics to be corrected in the single-color calibration beforestarting the multi-color calibration to correct multi-colorcharacteristics. Then, the image processing system according to thepresent exemplary embodiment performs the multi-color calibrationprocessing only when the evaluation result is good. Thus, it becomesfeasible to improve the correction accuracy in the multi-colorcalibration.

Further, if it is necessary to re-execute the calibration processingbecause of inappropriateness in the quality of an image printed aftercompleting the multi-color calibration, the image processing systemaccording to the present exemplary embodiment can re-execute only themulti-color calibration processing because there is not any problem inthe gradation characteristics. Therefore, it becomes feasible to shortenthe working time in re-executing the calibration processing in a casewhere the correction result was inappropriate in the calibrationincluding at least multi-color calibration.

Further, the image processing system according to the present exemplaryembodiment determines whether the maximum density evaluation result isNG if the gradation characteristics evaluation result is NG. If it isdetermined that the maximum density correction is appropriate, the imageprocessing system skips the maximum density correction processing inperforming the single-color calibration. Thus, the working efficiencycan be improved.

An image processing system according to the third exemplary embodimentregenerates a single-color calibration chart to be printed based on anevaluation result in a case where a single-color gradationcharacteristics evaluation result of the printer 115 is NG. Then, theimage processing system according to the present exemplary embodimentperforms single-color calibration using the regenerated chart.

In the above-mentioned exemplary embodiment, the CPU 103 performs thesingle-color calibration processing again if the gradationcharacteristics evaluation result of a printer is NG.

However, even in a case where the gradation characteristics evaluationresult is NG, there is a possibility that the gradation characteristicsevaluation result of only a specific color is NG. In this case,re-executing the single-color calibration for all of the evaluatedcolors is not efficient and not desired because color materials (e.g.,toners) are excessively or uselessly consumed.

Considering the above-mentioned situation, the image processing systemaccording to the present exemplary embodiment regenerates a chart for asingle-color if the gradation characteristics evaluation result is NG orif both the gradation characteristics evaluation result and the maximumdensity evaluation result are NG. Then, the image processing systemaccording to the present exemplary embodiment performs single-colorcalibration processing using the regenerated chart.

FIG. 11 is a flowchart illustrating an example procedure of theprocessing that can be performed by the image processing systemaccording to the present exemplary embodiment. The CPU 103 provided inthe controller 102 performs the processing of the flowchart illustratedin FIG. 11. The storage device 121 stores the acquired data. Further,the display device 118 displays a UI screen that includes an instructionmessage directed to a user. The input device 120 receives an instructionfrom the user.

Processing to be performed in step S1101 to step S1109 is similar to theprocessing performed in steps S601 to S609 and therefore redundantdescription thereof will be avoided.

Next, in step S1110, the CPU 103 evaluates the gradation characteristicsand the maximum density based on the extracted single-color density datawith reference to a predetermined target value “D” 1111, an evaluationcoefficient 1112, and an evaluation threshold value (i.e., gradationcharacteristics and maximum density) 1113.

Then, the CPU 103 outputs a gradation characteristics evaluation resultand a maximum density evaluation result 1118. The gradationcharacteristics evaluation result and the maximum density evaluationresult 1118 can be acquired by calculating the evaluation value Esaccording to the formula (I) for each color. The evaluation result 1118is usable to identify a color whose gradation characteristics result isNG.

Next, in step S1114, the CPU 103 determines whether the gradationcharacteristics evaluation result is NG. If it is determined that thegradation characteristics evaluation result is OK (no in step S1114),then in step S1116, the CPU 103 performs multi-color calibrationprocessing. If it is determined that the gradation characteristicsevaluation result is NG (yes in step S1114), then in step S1115, the CPU103 causes the display device 118 to display the error message screen901 illustrated in FIG. 9. Subsequently, in step S1120, the CPU 103acquires the maximum density evaluation result with reference to theevaluation result 1118.

If it is determined that the maximum density of the density dataextracted in step S1109 is equal to or less than the threshold value,the maximum density evaluation result 1118 of the printer 115 that hasprinted the chart “D” 1106 becomes OK. More specifically, the CPU 103determines that the maximum density has been appropriately corrected inthe single-color calibration. On the other hand, if it is determinedthat the maximum density of the extracted density data is greater thanthe threshold value, the maximum density of the printer 115 that hasprinted the chart “D” 1106 greatly deviates from the target value.Therefore, the maximum density evaluation result 1118 becomes NG. Morespecifically, the CPU 103 determines that the maximum density has notbeen appropriately corrected.

If the maximum density evaluation result is NG (yes in step S1120), theoperation returns to step S1101 because it is necessary to furthercorrect the maximum density. After completing the single-colorcalibration to correct the maximum density, the CPU 103 startssingle-color calibration to correct the gradation characteristics. Inthis case, to re-execute the single-color calibration, the CPU 103 cancontrol the display device 118 to display the UI screen illustrated inFIG. 12 to enable a user to instruct performing the single-colorcalibration again. Alternatively, the CPU 103 can automatically startthe single-color calibration again.

Further, if it is determined to re-execute the single-color calibration(yes in step S1120), then in step S1117, the CPU 103 regenerates chartdata with reference to the gradation characteristics evaluation result1118 and causes the printer 115 to output a chart based on theregenerated chart data. The chart data re-generated in step S1117includes only the data of a color whose gradation characteristicsevaluation value acquired from the evaluation result 1118 is determinedas being NG. Based on the printed regenerated chart data, the CPU 103performs the single-color correction in step S1101 and performs thegradation correction in step S1102.

Further, if it is determined that the maximum density evaluation resultis OK (no in step S1120), the CPU 103 determines that the maximumdensity has been appropriately corrected. Accordingly, the operationreturns to step S1102 to perform the single-color calibration to correctthe gradation characteristics.

In this case, it is useful that the CPU 103 controls the display device118 to display a UI screen that notifies a user of skipping the maximumdensity correction because the maximum density is currently appropriate.

As described above, when the CPU 103 performs the single-colorcalibration again while skipping the maximum density correction, the CPU103 regenerates chart data with reference to the gradationcharacteristics evaluation result 1118 in step S1119 and causes theprinter 115 to output a chart based on the regenerated chart data. Thechart data re-generated in step S1119 includes only the data of a colorwhose gradation characteristics evaluation value acquired from theevaluation result 1118 is determined as being NG. Based on the printedregenerated chart data, the CPU 103 performs single-color calibrationprocessing to correct the gradation characteristics in step S1102.

The image processing system according to the present exemplaryembodiment acquires a gradation characteristics evaluation result foreach color. However, it is also useful that the image processing systemacquires a gradation characteristics evaluation result for each density(e.g., low density, middle density, or high density) level andregenerates chart data based on the data whose evaluation result isdetermined as being NG. Further, it is also useful that the imageprocessing system regenerates chart data based on two types of (e.g.,color and density) information.

The image processing system according to the present exemplaryembodiment evaluates gradation characteristics to be corrected in thesingle-color calibration before starting the multi-color calibration tocorrect multi-color characteristics. Then, the image processing systemperforms the multi-color calibration processing only when the evaluationresult is good. Thus, it becomes feasible to improve the correctionaccuracy in the multi-color calibration.

Further, if it is necessary to re-execute the calibration processingbecause of inappropriateness in the quality of an image printed aftercompleting the multi-color calibration, the image processing system canre-execute only the multi-color calibration processing because there isnot any problem in the gradation characteristics. Therefore, it becomesfeasible to shorten the working time in re-executing the calibrationprocessing in a case where the correction result was inappropriate inthe calibration including at least multi-color calibration.

Further, the image processing system according to the present exemplaryembodiment regenerates chart data dedicated to the single-colorcalibration for data if it is determined that the gradationcharacteristics evaluation result is NG or if it is determined that boththe gradation characteristics evaluation result and the maximum densityevaluation result are NG. Thus, the color materials (e.g., toners) arenot excessively or uselessly consumed. The calibration can beefficiently performed.

<Other Exemplary Embodiment>

The present invention can be realized by executing the followingprocessing. More specifically, the processing includes supplying asoftware program that can realize the functions of the above-mentionedexemplary embodiments to a system or an apparatus via a network or anappropriate storage medium, and causing a computer (or a CPU or amicro-processing unit (MPU)) of the system or the apparatus to read andexecute the program.

Further, the present invention is applicable to an inkjet printer or athermal printer although the above-mentioned exemplary embodiment hasbeen described based on an electrophotographic apparatus. The scope ofthe present invention is not limited to a specific printer type.Further, the toner is an example of the recording agent usable inelectrophotographic printing. However, any other appropriate recordingagent (e.g., ink) is usable in the printing. The scope of the presentinvention is not limited to a specific recording agent type.

Other Embodiments

Embodiments of the present invention can also be realized by a computerof a system or apparatus that reads out and executes computer executableinstructions recorded on a storage medium (e.g., non-transitorycomputer-readable storage medium) to perform the functions of one ormore of the above-described embodiment(s) of the present invention, andby a method performed by the computer of the system or apparatus by, forexample, reading out and executing the computer executable instructionsfrom the storage medium to perform the functions of one or more of theabove-described embodiment(s). The computer may comprise one or more ofa central processing unit (CPU), micro processing unit (MPU), or othercircuitry, and may include a network of separate computers or separatecomputer processors. The computer executable instructions may beprovided to the computer, for example, from a network or the storagemedium. The storage medium may include, for example, one or more of ahard disk, a random-access memory (RAM), a read only memory (ROM), astorage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2012-172024, filed Aug. 2, 2012, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image processing apparatus comprising: animage forming unit configured to form an image; a measuring unitconfigured to measure the image formed by the image forming unit; acontrol unit configured to control execution of a single-colorcalibration to be performed to correct single-color reproductioncharacteristics of the image forming unit based on a measuring resultobtained when the measuring unit measures a single-color image formed bythe image forming unit with a single-color recording agent, andexecution of a multi-color calibration to be performed to correctmulti-color reproduction characteristics of the image forming unit basedon a measuring result obtained when the measuring unit measures amulti-color image formed by the image forming unit with a plurality ofcolor recording agents; an acquisition unit configured to, in responseto receiving an instruction for causing the control unit to successivelyexecute the single-color calibration and the multi-color calibration,cause the measuring unit to measure a single-color image formed by theimage forming unit after the single-color calibration has been executedby the control unit, and then acquire a difference between a targetvalue for evaluating the single-color reproduction characteristics and ameasured value obtained by measuring the single-color image formed bythe image forming unit after the single-color calibration; an evaluationunit configured to evaluate the single-color reproductioncharacteristics by using the difference acquired by the acquisitionunit; and a switch unit configured to, if the evaluation unit evaluatesthe single-color reproduction characteristics as being appropriate basedon the difference acquired by the acquisition unit, cause the controlunit to execute the multi-color calibration according to the receivedinstruction, and if the evaluation unit evaluates the single-colorreproduction characteristics as being inappropriate based on thedifference acquired by the acquisition unit, switch processing so as tocause the control unit to execute the single-color calibration againwithout following the received instruction.
 2. The image processingapparatus according to claim 1, wherein the acquisition unit isconfigured to acquire a difference between a gradation value of thesingle-color image formed by the image forming unit after thesingle-color calibration and a target value for evaluating thesingle-color reproduction characteristics, the target valuecorresponding to the gradation value, and the control unit is configuredto perform the single-color calibration again if the evaluation unitevaluates that the gradation value of the single-color image formed bythe image forming unit after the single-color calibration isinappropriate.
 3. The image processing apparatus according to claim 2,wherein the evaluation unit is configured to evaluate that the gradationvalue of the single-color image formed by the image forming unit afterthe single-color calibration is inappropriate if it is determined thatthe difference is greater than a threshold value.
 4. The imageprocessing apparatus according to claim 1, wherein the measuring unit isconfigured to measure a chart formed by the image forming unit after thecontrol unit completes the single-color calibration, and the evaluationunit is configured to evaluate a gradation of a single color obtained asa result of the measurement.
 5. The image processing apparatus accordingto claim 4, wherein the number of patches included in the chart formedby the image forming unit after the control unit completes thesingle-color calibration is smaller than the number of patches to beprinted on a chart used when the control unit performs the single-colorcalibration.
 6. The image processing apparatus according to claim 1,wherein a chart to be formed by the image forming unit to enable theevaluation unit to evaluate a gradation of the single color after thecontrol unit completes the single-color calibration is printed togetherwith a chart to be generated to perform the multi-color calibration onthe same paper.
 7. The image processing apparatus according to claim 1,wherein the acquisition unit is configured to acquire a differencebetween a maximum density value of the single-color image formed by theimage forming unit after the single-color calibration and a target valuefor evaluating the single-color reproduction characteristics, the targetvalue corresponding to the maximum density value, and the control unitis configured to perform the single-color calibration again if theevaluation unit evaluates that the maximum density value of thesingle-color image formed by the image forming unit after thesingle-color calibration is inappropriate.
 8. The image processingapparatus according to claim 7, wherein the evaluation unit isconfigured to evaluate that the maximum density value of thesingle-color image formed by the image forming unit after thesingle-color calibration is inappropriate if it is determined that thedifference is greater than a threshold value.
 9. The image processingapparatus according to claim 1, wherein the evaluation unit isconfigured to evaluate a maximum density of a single color obtained whenthe measuring unit measures a chart formed by the image forming unitafter the control unit completes the single-color calibration.
 10. Theimage processing apparatus according to claim 1, wherein the acquisitionunit is configured to acquire a first difference between a gradationvalue of the single-color image formed by the image forming unit afterthe single-color calibration and a target value for evaluating thesingle-color reproduction characteristics, the target valuecorresponding to the gradation value, and a second difference between amaximum density value of the single-color image formed by the imageforming unit after the single-color calibration and a target value forevaluating the single-color reproduction characteristics, the targetvalue corresponding to the maximum density value, and the control unitis configured to perform the single-color calibration again whilecorrecting a gradation value of an image formed by the image formingunit, without correcting a maximum density value of the image formed bythe image forming unit, if the evaluation unit evaluates by using thesecond difference that the maximum density value of the single-colorimage formed by the image forming unit after the single-colorcalibration is appropriate even when the evaluation unit evaluates byusing the first difference that the gradation value of the single-colorimage formed by the image forming unit after the single-colorcalibration is inappropriate.
 11. The image processing apparatusaccording to claim 1, wherein if the evaluation unit evaluates that thesingle-color reproduction characteristics of a specific color areinappropriate, the control unit is configured to perform thesingle-color calibration again using a chart formed by the image formingunit with the corresponding single-color.
 12. A calibration method foran image processing apparatus, comprising: forming a single-color imagewith a single-color recording agent; measuring the formed single-colorimage; performing a single-color calibration to correct single-colorreproduction characteristics of the forming based on a measuring resultobtained by the measuring; measuring a single-color image formed by theforming after the single-color calibration has been performed, and thenacquiring a difference between a target value for evaluating thesingle-color reproduction characteristics and a measured value obtainedby measuring the single-color image formed after the single-colorcalibration, in response to receiving an instruction for successivelyexecuting the single-color calibration and the multi-color calibration;evaluating the single-color reproduction characteristics by using theacquired difference; performing, after the evaluating, a multi-colorcalibration to correct multi-color reproduction characteristics of theforming based on a measuring result obtained when the measuring measuresa multi-color image formed by the forming with a plurality of colorrecording agents; executing the multi-color calibration according to thereceived instruction if the single-color reproduction characteristicsare evaluated as being appropriate based on the acquired difference; andswitching processing so as to execute the single-color calibration againwithout following the received instruction if the single-colorreproduction characteristics are evaluated as being inappropriate basedon the acquired difference.
 13. A non-transitory computer readablestorage medium storing a program that causes an image processingapparatus to perform a calibration method, the program comprising:computer-executable instructions for forming a single-color image with asingle-color recording agent; computer-executable instructions formeasuring the formed single-color image; computer-executableinstructions for performing a single-color calibration to correctsingle-color reproduction characteristics of the forming based on ameasuring result obtained by the measuring; computer-executableinstructions for measuring a single-color image formed by the formingafter the single-color calibration has been performed, and thenacquiring a difference between a target value for evaluating thesingle-color reproduction characteristics and a measured value obtainedby measuring the single-color image formed after the single-colorcalibration, in response to receiving an instruction for successivelyexecuting the single-color calibration and the multi-color calibration;computer-executable instructions for evaluating the single-colorreproduction characteristics by using the acquired difference;computer-executable instructions for performing, after the evaluating, amulti-color calibration to correct multi-color reproductioncharacteristics of the forming based on a measuring result obtained whenthe measuring measures a multi-color image formed by the forming with aplurality of color recording agents; computer-readable instructions forexecuting the multi-color calibration according to the receivedinstruction if the single-color reproduction characteristics areevaluated as being appropriate based on the acquired difference; andcomputer-readable instructions for switching processing so as to executethe single-color calibration again without following the receivedinstruction if the single-color reproduction characteristics areevaluated as being inappropriate based on the acquired difference.